A conventional power transmitting system for actuating a camshaft by using an endless chain or endless belt often includes an idler sprocket or pulley which is typically rotatably supported by a fixed shaft member affixed to an end surface of a cylinder block. A cylindrical bearing metal fitted into a central opening of the sprocket or the like typically forms a radial journal bearing in cooperation with the fixed shaft member.
As an arrangement for lubricating such a radial journal bearing, it is known to feed lubricating oil from an internal oil passage formed in the cylinder block to a radial bearing interface between the outer circumferential surface of the shaft member and inner circumferential surface of the bearing metal fitted in the central opening of the sprocket or the like. The bearing metal may be provided with a radial oil opening for feeding the lubricating oil to the radial bearing interface. See Japanese UM laid open publication No. 06-18009 (patent document 1) and Japanese patent laid open publication No. 2002-201924 (patent document 2).
When the lubricating oil for lubricating the sprocket is drawn from an internal oil passage formed in the cylinder block, the need for such an internal oil passage complicates the structure of the cylinder block, and this causes difficulty in the engine design and increases the manufacturing cost. Also, the limitation on the available space for the internal oil passage in the cylinder block may result in undesirably extended lengths of oil passages, and this may prevent a favorable feeding of lubricating oil to the radial journal bearing.
It is also known to spray an oil jet ejected from an oil jet nozzle projecting from a cylinder block onto a part of a sprocket (connected to an end of a crankshaft) at which the timing chain comes to mesh with the sprocket. See Japanese UM laid open publication No. 63-147511 (patent document 3).
The lubricating oil ejected from the oil jet nozzle may be able to favorably lubricate the exterior part of the sprocket such as the part thereof coming to mesh with the timing chain, but unable to lubricate the radial bearing interface between the fixed shaft member and sprocket in the case of an idler sprocket.